1. Field of the Invention
The present invention relates to a molding die which is used for an injection molding, a blow molding and the like in addition to various kinds of casting such as a die casting, a low pressure die casting, a gravity casting and the like, and a die changing method of the same.
2. Description of the Related Art
In a recent production line, a large item small scale production is generalized, and a cycle for replacing a die has become significantly short. Further, a product formed by the casting, the injection molding or the like is becoming more complex or larger in size, which makes it impossible to avoid shortening of a service life of the die, thereby increasing a frequency of replacement. In particular, in the die casting, since a high temperature molten metal is charged within the die at a high speed and a high pressure, the die is seriously damaged, thus requiring highly frequent replacement of the die.
Therefore, recently, die constituting elements such as a fixed die, a movable die and the like are separated into a commonly formed general portion and an exclusive portion forming a cavity, so that the die changing is performed by replacing only the exclusive portion (for example, Japanese Patent Laid-Open Publication Nos. 9-70653, 9-122871 and 1-271213, and the like).
However, in accordance with the conventional die changing method in which only the exclusive portion is replaced, the general portion and the exclusive portion are integrally removed from a molding machine, and are taken to outside the molding machine, and then the exclusive portion is replaced. Accordingly, in this case, a troublesome work of taking out the general portion from the molding machine still remains, and particularly in the case of the die for the die casting, it is necessary to attach and detach a complex cooling system for cooling inside the die and a control system, and there is a problem that a die changing time can not be totally shortened significantly. Further, for example, obtaining a large-sized die cast product with a complex structure such as a cylinder block, requires a slide, and thus the total die becomes heavy (196 kN (about 20 tons) for one example) and large in size (about 2 m for one example). As a result, not only has it become extremely troublesome to take out the die from the molding machine, but also it is necessary to take out and insert a tie bar connecting a fixed portion to a movable portion, creating a problem that only extremely little effect can be obtained in shortening of the die changing time.
Meanwhile, in a structure disclosed in Japanese Patent Laid-Open Publication No. 6-190531, only a part (a core) of the exclusive portion is replaced while leaving the general portion in the molding machine. According to this structure, however, since the exclusive portion is fastened by bolts, it is necessary to perform the fastening operation within the molding machine with a limited space, and a deterioration in workability and a unsafe operation can not be avoided. Further, since the bolts are tightened to the exclusive portion from a front surface thereof, this structure can not be applied to the exclusive portion whose front surface constitutes the cavity forming surface, thereby limiting an applicable range of such structure.